Ultracold Neutron Production at Compact Neutron Sources

We propose a new concept for ultracold neutron (UCN) production using a compact neutron source. The essential idea is to surround a volume of superfluid helium with a "supercold" moderator in the vicinity of a low-radiation neutron production target from (p,n) reactions. The supercold moderator should possess a peak brightness near the single-phonon excitation band of the superfluid helium for UCN at 1 meV. This would maximize UCN production in the UCN converter with the limited flux available from a compact neutron source. We report the conceptual design of a compact UCN source system to demonstrate that such a small UCN source can be operated at a compact pulsed neutron source facility. The estimated UCN production rate is as high as ~80 UCN/cc/s when the brightness of the supercold moderator peaks at 1 meV. The main advantages of this compact UCN source include the competitive rate of UCN production, the very low radiative and thermal loads on the UCN source, the relatively low cost of operation, and easy accessibility to the experimental area. Although no such supercold moderator has yet been demonstrated, promising materials for the supercold moderation medium exist.